Down-the-hole rock drill

ABSTRACT

A down-the-hole rock drill includes a top sub, a driver sub having a bore therein, and a piston case extending between and detachably connected to the top sub and the driver sub. A piston is located within the piston case, and a drill device is detachably connected to the driver sub. The drill device includes a shank and a head. The drill device also has a central passageway for a flushing medium. A tube is secured in the central passageway at a free end of the shank. The tube extends beyond the free end of the shank, and the piston has a central piston passageway that receives the tube. The piston is slidably movable relative to the tube. A first portion of the shank located closest to the head has a cross section, normal to a longitudinal center axis of the shank, in the shape of a multi-lobed figure that is continuously non-concave, and the bore of the driver sub is of a matching cross-sectional shape. In addition, the drill device is secured axially by a bit retainer that symmetrically cooperates with a circumferentially extending shoulder on a second portion of the shank. The second portion being located closest to the free end of the shank.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The present invention refers to a down-the-hole rock drill.

b. Description of Related Art

The most common way by far to provide rotational driving between theshaft of a drill bit and a driver sub is to use splines both on theexterior of the shaft and on the wall of the bore of the driver sub.However, such a design of the cooperating rotational driving means ofthe shaft of the drill bit and the bore of the driver sub is complicatedto manufacture and consequently the manufacturing is time consuming andexpensive. According to GB-B-1 242 052 the conventional splines designsuffers from the disadvantage that the splines of the chuck (driver sub)and the drill bit are caused to wear very rapidly by the repeatedrelative axial and angular movements between them.

From GB-B-1 242 052 a percussive rock drilling apparatus of the typedefined above in the first paragraph is previously known. The aim of thedesign of the rotational driving means between the driver sub and theshaft of the drill bit as disclosed in GB-B-1 242 052 is to avoid saiddisadvantages concerning rapid wear and angular movements.

The known device according to GB-B-1 242 052 has a transverse pinsecured in the driver sub (chuck) of the device, said pin cooperatingwith an axially extending flat surface on the shaft of the drill bit torestrict the axial displacement of the drill bit. However, such astructural design of the means for restriction of axial displacement ofthe drill bit relative to the driver sub will negatively affect thelongitudinal centering of the shaft, during working conditions, relativeto the bore of the driver sub. This is an extremely important featurefor drill bits having an internal bore extending axially through thedrill bit, i.e. drill bits of the type used in the down-the-hole rockdrill according to the present invention. If, during working conditions,the shaft of the drill bit is not properly centered, relative to thebore of the driver sub, then there will be problems in the cooperationbetween the piston and the drill bit as regards the foot valve and theenergy transmission.

Since the cooperation of the rotational driving means of the driver suband the drill bit of GB-B-1 242 052 do not provide a longitudinalcentering of the drill bit relative to the bore of the driver sub it isnecessary to provide additional guiding means for the driver sub at thetransition between the shaft and the head of the drill bit. Theprovision of such additional guiding means will of course negativelyaffect the manufacturing costs of the drill bit compared to a drill bithaving no such guiding means.

OBJECTS AND SUMMARY

An object of the present invention is to present a down-the-hole rockdrill having a drill bit including a shaft that is perfectly centeredduring working conditions relative to the bore of the driver sub.

A further object of the present invention is that according to apreferred embodiment of the present invention the guiding means at thebottom and/or top of the shaft of the drill bit are eliminated.

Another object of the present invention is to improve the radiusedtransmission between the shaft and the head of the drill bit.

Yet another object of the present invention is to improve the cooling ofthe interacting surfaces of the shaft of the drill bit and the bore ofthe driver sub.

Yet another object of the present invention is to achieve a lessexpensive manufacturing of the shaft of the drill bit and the bore ofthe driver sub.

The present invention refers to a down-the-hole rock drill including atop sub, a driver sub, a piston case extending between and detachablyconnected to said top sub and said driver sub, a piston located withinsaid piston case, a drill bit detachably connected to said driver sub,said drill bit including a shank and a head, the drill bit having acentral bit passageway for flushing medium and a number of branchpassageways for flushing medium, said branch passageways extending fromthe central bit passageway to the front of the head, a tube means beingsecured in the central bit passageway, said tube means extending beyondthe upper end of the drill bit, the piston having a central pistonpassageway that receives said tube means, said piston being slidablymovable relative to said tube means.

BRIEF DESCRIPTION OF THE DRAWINGS

Below embodiments of the present invention will be described, referencebeing made to the accompanying drawings, where FIG.1 is a sectionthrough a lower part of a down-the-hole rock drill according to thepresent invention;

FIG. 2a is a section along IIa--IIa in FIG. 1; FIG. 2b is across-section of a first portion of a shank of a drill bit;

FIG. 3 is an exploded perspective view of an eccentric drill tool havinga shank in accordance with the present invention; and

FIGS. 4a-4e are alternative embodiments of the cross-section of a firstportion of a shank of a drill bit.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In FIGS. 1, 2a and 2b a preferred embodiment of the lower part of adown-the-hole rock drill 10 according to the present invention isdisclosed. Said down-the-hole rock drill 10 has a longitudinal centreaxis L. A generally cylindrical piston case 11 has an internal thread 12at its lower end. A driver sub 13 has a lower portion 14 of the sameouter diameter as the piston case 11. The upper portion 15 of the driversub 13 has a reduced outer diameter, said upper portion 15 having anexternal thread 16 that in assembled state is adapted to engage theinternal thread 12 of the piston case 11.

The driver sub 13 further has an internal bore 17 that is adapted toreceive a shank 18 of a drill bit 19, said drill bit 19 furtherincluding a head 20 connected to the shank 18. Said head 20 is ofconventional design and thus not forming a part of the presentinvention.

In the disclosed embodiment of FIGS. 1, 2a and 2b a first portion 18a ofthe shank 18, said first portion 18a being located closest to the head20, has a regular cross-sectional shape with three convex lobes 18c andconvex sides 18d connecting said lobes 18c. The bore 17 is ofcomplementary cross-section to that of the first portion 18a of theshank 18.

In FIG. 2b said cross-sectional shape with three convex lobes of thefirst portion 18a is further defined. The convex lobes 18c have a radiusof curvature r and the convex sides 18d have a radius of curvature R,said radius r being essentially smaller than said radius R. Thecross-section of the first portion 18a has a further characteristic inthat the distance between two parallel tangents to the periphery of saidcross-section is always constant. In pertinent technical literature sucha cross-sectional shape is denoted as a P3 profile.

There is of course a certain radial play between the bore 17 and thefirst portion 18a of the shank 18 although said radial play isconsiderably smaller than the radial play of a conventional splinesconnection. In the disclosed embodiment the regular cross-sectionalshape with three convex lobes (P3) of the first portion 18a of the shank18 reaches all the way to the head 20.

The second portion 18b of the shank 18, said second portion 18b beinglocated closest to the free end of the shank 18, has a cylindricalcross-sectional shape and also includes a circumferential shoulder 21that cooperates with a bit retainer ring 22 that rests against the upperend of the driver sub 13. The bit retainer ring 22 consists of twohalves and prevents the bit 19 from axially falling out of the driversub 13.

The shank 18 of the drill bit 19 is provided with a central, axiallyextending, bore forming a central bit passageway 23 for the flushingmedium, said passageway 23 extending a limited distance into the drillhead 10. A number of bores 24 extend from the front surface 25 of thedrill head 10 to the bit passageway 23, said bores forming branchpassageways 24 for the flushing medium, said branch passageways 24having an angled extension relative to the longitudinal centre axis L ofthe device 10.

At the free end of the shank 18 a foot valve 26 is mounted, said footvalve 26 extending a limited distance into the central bit passageway23.

Above the drill bit 19 a piston 27 is provided, said piston 27 beingreciprocably movable in axial direction within the piston case 11. Saidpiston 27 is provided with a central, axially extending, bore forming acentral piston passageway 28 for the flushing medium. When the piston 27rests against the upper end of the drill bit 19 the foot valve 26extends into the central piston passageway 28, the relative dimensionsbetween the foot valve 26 and the central piston passageway 28 beingsuch that the piston 27 is movable by slide fit relative to the footvalve 26.

As is evident from FIG. 2a the internal bore 17 of the driver sub 13 isprovided with a number of lubricating/venting grooves 29. The grooves 29have an axial extension only in the lower part of the internal bore 17of the driver sub 13. This is necessary since when the drill bit 19 isin its working position according to FIG. 1 there should be no freepassageway between the shank 18 and the internal bore 17. However, whenthe drill bit 19 is in its open position, i.e. the shoulder 21 of thedrill bit 19 rests against the bit retaining ring 22, then it isnecessary to have a free passageway between the shaft 18 of the drillbit 19 and the internal bore 17 of the driver sub 13 since otherwise thereciprocal motion of the piston 27 will continue even when the drill bit19 is in its open position.

The grooves 29 may have a helical extension in axial direction of thedriver sub 13. Within the scope of the present invention it is alsopossible to provide lubricating/venting grooves (not shown) on the firstportion 18a of the shank 18 of the drill bit 19. In analogy with whathas been stated above regarding a free passageway between the shank 18and the internal bore 17 such lubricating/venting grooves must extendaxially only in the upper part of the first portion 18a. Thelubricating/venting grooves on the first portion 18a may also have ahelical extension in axial direction of the shank 18. Thelubricating/venting grooves on the first portion 18a can replace thegrooves 29 or be in combination with these.

It should be pointed out that the lubricating/venting arrangementsdescribed above are only examples of preferred embodiments. Thus, withinthe scope of the present invention other lubricating/ventingarrangements than those described above are possible.

The improved function of the down-the-hole rock drill due to thefeatures of the present invention is the following. When thedown-the-hole rock drill is working the piston case 11 is rotated by apower source at the ground level. The piston case 11 will then confer arotational driving to the shank 18 of the drill bit 19 due to thecomplementary shape of the cross-section of the first portion 18a of theshank 18 of the drill bit 19 and the internal bore 17 of the driver sub13. The fact that said interaction between the first portion 18a of theshank 18 and the bore 17 takes place over a considerable length of theshank 18 and the fact that the complementary-shaped cross-section ofsaid portions is a regular will result in a proper centering in axialdirection of the shank 18 relative to the driver sub 13. This means thatnormally there is no need for additional centering means between theshank 18 and the driver sub 13.

Since the shank 18 has a proper centering relative to the driver sub 13the cooperation between the foot valve 26 and the central pistonpassageway 28 of the piston 27 will be improved. When the piston 27 isin its uppermost position then the lower end of the piston 27 will belocated above the upper end of the foot valve 26. When the piston 27moves downwardly then the upper end of the foot valve 26 will enter thecentral piston passageway 28 at a certain stage. At that stage it isvery important that the shank 18 is properly centered relative to theinternal bore 17 of the driver sub 13 since otherwise the foot valve 26may be damaged and/or subjected to stresses. Thus the centering featureof the present invention will reduce the friction forces between thefoot valve 26 and the piston passageway 28. This is important both froma functional point of view and also as regards the length of life forthe foot valve 26.

The transfer of percussive energy between the piston 27 and the drillbit 19 will also be improved if the shank 18 is properly centeredrelative to the internal bore 17 of the driver sub 13. Said centeringwill establish a full area contact between the lower end of the piston27 and the upper end of the drill bit 19 when the piston 27 hits thedrill bit 19.

The first portion 18a of the shank 18 and the internal bore 17 of thedriver sub 13 are preferably manufactured by noncircular turning. Sincethe cross-section of said details has rather large radii the stressconcentration will be reduced as compared to a conventional splinesdesign. This also means that the creation of martensite due to frictionis reduced.

In the disclosed embodiment the foot valve 26 is a tubular element of arather limited axial extension. However, in the art there is also knowna down-the-hole rock drill having a tubular element that has one endextending into the central bit passageway and the other end of thetubular element extending beyond the upper end of the piston, i.e. thetubular element extends through the piston. In such a design both thedrill bit and the piston are movable relative to the tubular element byslide fit. The tubular element is secured axially at a location abovethe piston. The present invention is also applicable to down-the-holerock drills of that type.

As is evident from FIG. 1 the first portion 18a of the shank 18, saidfirst portion 18a having a cross-sectional shape in accordance with apreferred embodiment of the present invention, extends all the way up tothe head 20 of the drill bit 19. However, within the scope of thepresent invention it is possible to have an alternative transitionbetween the first portion 18a and the head 20, e.g. a cylindricalportion. The axial extension of such cylindrical portion shouldpreferably be rather limited and the axial extension of the firstportion 18a must always be sufficient to provide the centering/guidingfunction as described above.

In FIG. 3 the present invention is applied to an eccentric drill toolfor a down-the-hole hammer. The drill tool according to FIG. 3 has aguide device 19' that includes a head 20' and a shank 18' having a firstportion 18'a located closest to the head 20' and a second portion 18'blocated closest to the free end of the shank 18'. The second portion18'b has a shoulder 21'. The shank 18' of the guide device 19' in FIG. 3corresponds to the shank 18 of the drill bit 19 in FIG. 1. The shank 18'is in the same way as the shank 18 received in a driver sub and securedaxially by a retaining ring. In the same manner as the arrangement ofFIG. 1 the driver sub is connected to a casing of a down-the-hole rockdrill. The shank 18' has a central guide device passageway (not shown)extending axially through the guide device 19'. A foot valve 26' ismounted at the free end of the shank 18' said foot valve 26' extendinginto the guide device passageway a limited distance.

In principle the same advantages concerning centering of the shank 18'in the bore of the driver sub and transfer of percussive energy betweenthe piston and the shank 18' of the guide device 19' apply to theembodiment of FIG. 3 as described above in connection with theembodiment of FIGS. 1 and 2(a,b). The first portion 18'a of the shank18' is preferably manufactured in the same way as the first portion 18aof the shank 18, i.e. by non-circular turning. Also the cross-sectionalshape of the first portion 18'a is equal to the cross-section shown inFIG. 2b.

The drill tool according to FIG. 3 further has a central pilot bit 30'that is detachably connected to the guide device by a thread coupling. Areaming bit 31' is mounted on the shank of the pilot bit 30' closest tothe head of said pilot bit 30'. The reaming bit 31' is rotatable alimited angle relative to the pilot bit 30'. The drill tool according toFIG. 3 is used for simultanously drilling and casing through overburden.

In FIGS. 4a-4e a number of alternative cross-sectional shapes of thefirst portion 18a,18'a of the shank 18,18' are shown.

FIG. 4a shows a cross-section in the shape of an ellipse.

FIG. 4b shows a cross-section that is a modification of thecross-section shown in FIG. 2, the difference being that the lobes aresomewhat flattened although still being convex. In pertinent technicalliterature the cross-section of FIG. 4b is denoted as a PC3 profile.

FIG. 4c shows a cross-section of generally square shape. In pertinenttechnical literature the cross-section of FIG. 4c is denoted as a P4profile.

FIG. 4d shows a cross-section of generally square shape. Compared to thefigure of FIG. 4c the figure of FIG. 4d has more flattenedlobes/corners. In pertinent technical literature the cross-section ofFIG. 4d is denoted as a PC4 profile.

FIG. 4e shows a cross-section that is a combination of a semi-ellipticand a semi-circular shape.

The profiles referred to above having a "P" prefix (e.g. P3 profile) areoften in pertinent technical literature called polygon profiles and theyare subject to a proposed DIN standard.

The basic concept of the present invention is a cross-section of thefirst portion 18a;18'a being a multi-lobed figure that is continuouslynon-concave. This definition is valid for all the embodiments of thefirst portion of the shank that are shown in this application.Preferably it is a regular figure, i.e. the sides are of equal length.

However, the invention is in no way restricted to the embodimentsdescribed above but can be varied freely within the scope of theappending claims.

We claim:
 1. A down-the-hole rock drill, comprising:a top sub, a driversub having a bore therein, a piston case extending between anddetachably connected to said top sub and said driver sub, a pistonlocated within said piston case, a drill device detachably connected tosaid driver sub, said drill device including a shank and a head, thedrill device having a central passageway means for a flushing medium, atube means being secured in the central passageway means at a free endof the shank. said tube means extending beyond the free end of theshank, the piston having a central piston passageway that receives saidtube means, said piston being slidably movable relative to said tubemeans, a first portion of the shank located closest to the head has across-section, normal to a longitudinal center axis of the shank, in theshape of a multi-lobed figure that is continuously nonconcave, and thatthe bore of the driver sub is of a matching cross-sectional shape, andthe drill device is secured axially by a bit retaining means thatsymmetrically cooperates with a circumferentially extending shouldermeans on a second portion of the shank, said second portion beinglocated closest to the free end of the shank.
 2. Down-the-hole rockdrill according to claim 1, wherein the cross-sectional shape of thefirst portion of the shank is regular.
 3. Down-the-hole rock drillaccording to claim 1, wherein the cross-sectional shape of the firstportion is continuously convex.
 4. Down-the-hole rock drill according toclaim 1, wherein the first portion of the shank has a three-lobedcross-sectional shape that is regular, and that the distance between twoparallel tangents to the periphery of said cross-section is constant. 5.Down-the-hole rock drill according to claim 1, wherein the bit retainingmeans is of annular shape, and that said bit retaining means at leastpartially surrounds the second portion and cooperates with a shouldermeans on said second portion on the shank.
 6. Down-the-hole rock drillaccording to claim 5, wherein the bit retaining means is in two pieces.7. Down-the-hole rock drill according to claim 1, wherein said drilldevice is a drill bit.
 8. Down-the-hole rock drill according to claim 7,wherein the first portion of the shank extends all the way to the headof the drill bit.
 9. Down-the-hole rock drill according to claim 1,wherein said drill device is a guide device.
 10. A drill bit adapted toconstitute a part of a down-the-hole rock drill, said drill bitcomprising:a shank and a head, the drill bit having a central bitpassageway for a flushing medium and a number of branch passageways forthe flushing medium, said branch passageways extending from the centralbit passageway to the front of the head, a first portion of the shankbeing located closest to the head has a cross-section, normal to alongitudinal center axis of the shank, in the shape of a multi-lobedfigure that is continuously nonconcave, a second portion of the shankbeing located closest to a free end of the shank is provided with acircumferentially extending shoulder means for cooperating with a bitretaining means.
 11. Drill bit according to claim 10, wherein the firstportion of the shank has a regular cross-sectional shape.
 12. Drill bitaccording to claim 10, wherein the first portion of the shank has across-sectional shape with three convex lobes and convex sidesconnecting said lobes.
 13. Drill bit according to claim 10, wherein thefirst portion of the shank has a four-sided cross-sectional shape. 14.Drill bit according to claim 10, wherein the central bit passageway, atits end directed to the free end of the shank, is designed to receive atube means.
 15. A guide device adapted to constitute a part of adown-the-hole rock drill, said guide device comprising:a shank and ahead, the guide device having a central guide device passageway meansfor a flushing medium, a first portion of the shank being locatedclosest to the head has a cross-section, normal to a longitudinal centeraxis of the shank, in the shape of a multi-lobed figure that iscontinuously nonconcave, a second portion of the shank, said portionbeing located closest to a free end of the shank, is provided with acircumferentially extending shoulder means for cooperating with a bitretaining means symmetrically arranged around the second portion of theshank.
 16. Guide device according to claim 15, wherein the first portionof the shank has a regular cross-sectional shape.
 17. Guide deviceaccording to claim 15, wherein the first portion of the shank has across-sectional shape with three convex lobes and convex sidesconnecting said lobes.
 18. Guide device according to claim 15, whereinthe first portion of the shank has a four-sided cross-sectional shape.19. Guide device according to claim 15, wherein the central guide devicepassageway, at its end directed to the free end of the shank, isdesigned to receive a tube means.